Communications is involved with the transfer of data. Data that is in a digital format often needs to be manipulated to achieve effective communication. The manipulation of data is often performed via operations. Some such operations are switching of data, merging of data, and demerging data. These operations may be performed at different physical and/or logical locations. For example, these locations may be, but are not limited to, a physical media interface, a media access controller (MAC), a datalink controller, network search engine, traffic manager. These are but examples of locations for digital format manipulation operations.
Three of the existing approaches for the switching and multiplexing of data between a Physical Media Interface and a Media Access Controller (MAC) are:
1. Direct connection between a Media Interface and a MAC;
2. Direct connection between a Media interface and a packet switch with integrated MAC function; and
3. Serialization and deserialization (bit interleaving) or byte interleaving of data between a Media Interface and a backplane.
These three are illustrated in FIG. 3, denoted 301, 302, and 303 respectively.
FIG. 3, at 301 illustrates a direct connection between a Media Interface and a MAC. This is described in the IEEE 802.3 standard. A Media interface is connected to a MAC via an interface known as the Media Independent interface (MII). The MAC is responsible for performing checking and filtering functions of received data frames and for transmitting data frames in accordance with the standard. A problem with this approach is that for multiple physical connections, a MAC function is required for each physical interface before the data can be multiplexed over a backplane via a system interface. Existing solutions adopt a system interface that is sufficient only for the aggregate bandwidth of the physical interfaces. The MAC and multiplexing function may add latency and complexity to the transfer of data to a backplane including additional flow control and data buffering. In addition, flow control or other MAC functions must be performed in the MAC devices. This adds complexity to the system configuration, control, and management functions. It may be appropriate for small systems with few physical ports and where the entire system can be implemented on a single circuit board; however, it does not “scale” well to larger systems having more ports and many different data processing and forwarding functions which must be carried out by special processors.
FIG. 3, at 302 illustrates a direct connection between a Media interface and an Ethernet or packet switch having an integrated MAC function, such as a Gigabit Ethernet MAC (GE MAC). This approach is described in manufacturers' (such as Broadcom's and Marvel's) literature. A physical layer device connects to a switch device through a local interface. A separate backplane interface is often provided, usually a high speed serial interface of a proprietary nature which may be regarded as a physical layer interface. A problem with this approach is that such switch devices are physically large due to the large number of Inputs/Outputs (I/Os), consume high power, and consequently create thermal problems. For systems having a high number of physical I/Os or functional circuit boards, their use will increase system configuration control and management complexity. In addition, a separate switch device is required to terminate all the high speed data streams, demultplex the data, and provide a further level of switching. This combination of switch devices that have local interfaces and switch devices that have high speed interfaces is also referred to as a switch fabric. Prior attempts to increase the efficiency of switch fabrics have resulted in data loss or large increases in latency. Prior attempts to decrease the number of signals and thereby increase the number of physical media interfaces that can be connected to a switch device has resulted in proprietary interfaces being substituted for interfaces defined in prior standards.
FIG. 3, at 303 illustrates a serialization and deserialization (bit interleaving) or byte interleaving of data between a media interface and a backplane wherein a parallel interface of a physical layer interface, such as a Gigabit Media Independent Interface (GMII) from a Network Processor Unit (NPU), is converted to a serial backplane interface in order to reduce the number of signals, clocking and wiring complexity of the backplane. In this case a MAC function is not required unless a combination or multiplexing of multiple physical interfaces is required according to the alternative prior approaches. A problem with serialization and deserialization and alternative variations of the prior approaches is that for multiple physical interfaces a technique will be required to synchronize multiple parallel interfaces with the serial backplane interface. This adds latency, increases the physical size of the circuit, complexity, and power.